The present invention relates to a method for preparing an ethylene polymer or copolymer, and more particularly a method for producing, by use of a catalyst of high activity, an ethylene polymer or copolymer with high bulk density and a narrow molecular weight distribution.
Magnesium-containing catalysts for production of ethylene polymer or copolymer are known to have very high catalytic activity and endow the produced polymer with a high bulk density. They are also known to be suitable for both liquid and gaseous reactions alike. The liquid polymerization of ethylene means the reaction taking place in the state of bulk ethylene or in a medium like isopentane and hexane, and in terms of the adaptability of a catalyst in such reactions its high activity and the resultant bulk density of a polymer are features of importance. A significant variable decisive of the properties of an ethylene polymer or copolymer, produced with the use of such a catalyst, is the molecular weight distribution. A narrow molecular weight distribution is very advantageous in later manufacture of injection products.
Many catalysts containing magnesium and titanium for production of olefin and the processes for production of these catalysts have been reported. In particular, many processes making use of magnesium solutions to obtain catalysts for polymerization of olefin which has a high bulk density, have been learned. They include processes to obtain magnesium solutions by reacting magnesium compounds with such electron donors as alcohol, cyclic ether, organic carboxyl acid, etc., in the presence of hydrocarbon solvents. Instances where alcohol was used are referred to in U.S. Pat. Nos. 4,330,649 and 5,106,807. Methods for producing a magnesium-carrying catalyst by reacting a magnesium solution with halogen compounds such as titanium tetrachloride are well known. There have also been efforts to control the catalyst""s activity and the polymer""s molecular weight distribution by addition of ester compounds. These catalysts have a merit in providing the polymer""s high bulk density, but their catalytic activity and the polymer""s molecular weight distribution have something yet to be improved. Tetrahydrofuran, a cyclic ester, has been used as a magnesium compound solvent in U.S. Pat. Nos. 4,477,639 and 4,518,706.
Meanwhile, U.S. Pat. Nos. 4,847,639, 4,816,433, 4,829,037, 4,970,186, and 5,130,284 have reported use of electron donors such as magnesium alkoxide, dialkylphthalate, phthaloyl chloride, etc., in reaction with a titanium chloride compound for production of catalysts with high catalytic activity and the resultant olefin""s improved bulk density.
U.S. Pat. No. 5,459,116 has reported a method for production of a titanium-carrying solid catalyst by reacting a magnesium solution containing an ester having at least one hydroxy group as electron donor with a titanium compound. By this method it is possible to obtain a catalyst which is excellent in catalytic activity, and provides the resultant polymer with high bulk density, but the polymer has something yet to be improved in its molecular weight distribution.
Use of external electron donors in polymerization of xcex1-olefin, especially polypropylene for improvement of stereoregularity, is generally known, and is, commercially, in wide use. As external electron donors, alkoxysilane compounds are widely known, but it is also known that, although the polymer""s stereoregularity improves with the use of these, generally the polymer""s molecular weight distribution becomes relatively broad. KP 93-665 has shown a way and its merit of rendering the polymer""s molecular weight distribution narrower by the use of organic silane as an external electron donor in polymerization of propylene.
An objective of the present invention is to provide a method and catalyst for production of an ethylene polymer or copolymer with a large bulk density, and a narrow molecular weight distribution; and more particularly, a method and catalyst for producing an ethylene polymer or copolymer of well-regulated granular forms, high polymerization activity, and a narrow molecular weight distribution.
The process of the embodiment described herein for producing an ethylene polymer or copolymer involves preparing a solid titanium complex catalyst in a simple yet effective process using magnesium, titanium, halogen, and an electron donor, by:
i. producing a magnesium compound solution by contact-reacting a halogenated magnesium compound and alcohol,
ii. reacting the said solution with an ester compound containing at least one hydroxy group and a silicon compound containing an alkoxy group, and
iii. adding thereto a mixture of a titanium compound and a silicon compound.
An ethylene polymerization or copolymerization is then performed with a compound of an organic metal of Group 2, 12, or 13 on the periodic table of elements by the use of the aforesaid catalyst in the presence of an alkoxy silane compound.
Examples of halogenated magnesium compounds which may be used in production of the catalyst include such dihalogenated magnesiums as magnesium chloride, magnesium iodide, magnesium fluoride, and magnesium bromide; such alkylmagnesium halides as methylmagnesium halide, ethylmagnesium halide, propylmagnesium halide, butylmagnesium halide, isobutylmagnesium halide, hexylmagnesium halide, and amylmagnesium halide; such alkoxymagnesium halides as methoxymagnesium halide, ethoxymagnesium halide, isopropoxymagnesium halide, butoxymagnseium halide, and octoxymagnesium halide; and such aryloxymagnesium halides as phenoxymagnesium halide and methylphenoxymagnesium halide, for example. Of the above-named compounds, a mixture of two or more may also be used. These magnesium compounds may also be used effectively when they are in the form of a complex with other metals.
The above-listed halogenated magnesium compounds may be represented by simple chemical formulae, but exceptions may arise from differences in the methods for. producing the magnesium compounds. In such cases, they generally may be regarded as mixtures of these listed magnesium compounds. For example, the compounds obtained by reacting a magnesium compound with a polysiloxane compound, a halogen-containing silane compound, or alcohol; or the compounds obtained by reacting a magnesium metal with alcohol, phenol, or ether in the presence of halosilane, phosphor pentachloride, or thionyl chloride may also be used. The preferable magnesium compounds are magnesium halides, especially magnesium chloride; alkylmagnesium chlorides, preferably those that have a C1xcx9cC10 alkyl group; alkoxy magnesium chlorides, preferably those that have a C1xcx9cC10 alkoxy group; and aryloxy magnesium chlorides, preferably those that have a C6xcx9cC20 aryloxy group.
Examples of hydrocarbon solvents which may be used here include, for example: aliphatic hydrocarbons, such as pentane, hexane, heptane, octane, decane or kerosene; alicyclic hydrocarbons such as cyclobenzene, methylcyclobenzene, cyclohexane, or methylcyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumen, and cymene; and halogenated hydrocarbons such as dichloropropane, dichloroethylene, trichloroethylene, carbon tetrachloride, and chlorobenzene.
In conversion of the above-listed halogenated magnesium compounds into a magnesium compound solution, alcohol is used in the presence or absence of the above-listed hydrocarbons. The kinds of alcohol include alcohols having 1xcx9c20 carbons, such as methanol, ethanol, propanol, butanol, benzene alcohol, phenylethyl alcohol, isopropylenebenzyl alcohol, and cumyl alcohol; and preferably alcohols that have 1xcx9c12 carbons. The size of granules of the catalyst and the granular distribution in the resultant polymer vary according to the kinds and total quantity of alcohol, the kinds of magnesium compound, the ratio of magnesium to alcohol, etc.; but the total quantity of alcohol required for use to obtain the necessary magnesium solution is at least 0.5 mol, preferably about 1.0xcx9c20 mols, and more preferably about 2.0xcx9c10 mols to one mol of the magnesium compound.
The reaction of a halogenated magnesium compound and alcohol in production of the magnesium compound solution is performed preferably in a hydrocarbon medium for about 15 minutes to 5 hours, preferably for about 30 minutes to 4 hours, at about xe2x88x9225xc2x0 C., preferably xe2x88x9210xcx9c200xc2x0 C., and more preferably at about 0xcx9c150xc2x0 C., though the temperature may vary according to the kind and quantity of alcohol in use.
The ester compounds that may be used as electron donors in production of the catalyst include, for example: unsaturated aliphatic acid esters containing at least one hydroxy group, such as 2-hydroxy ethylacrylate, 2-hydroxy ethylmethacrylate, 2-hydroxy propylacrylate, 2-hydroxy propylmethacrylate, 4-hydroxy butylacrylate, and pentaerythritol triacrylate; aliphatic monoesters and polyesters containing at least one hydroxy group, such as 2-hydroxy ethylacetate, methyl 3-hydroxy butylate, ethyl 3-hydroxy butylate, methyl 2-hydroxy isobutylate, ethyl 2-hydoxy isobutylate, methyl-3-hydroxy-2-methyl propionate, 2,2-dimethyl-3-hydroxy propionate, ethyl-6-hydroxy hexanoate, t-butyl-2-hydroxy isobutylate, diethyl-3-hydroxy glutarate, ethyl lactate, isopropyl lactate, butylisobutyl lactate, isobutyl lactate, ethylmandelate, dimethyl ethyl tartrate, ethyl tartrate, dibutyl tartrate, diethyl citrate, triethyl citrate, ethyl 2-hydroxy caproate, or diethyl bis-(hydroxy methyl) malonate; aromatic esters containing at least one hydroxy group, such as 2-hydroxy ethyl benzoate, 2-hydroxy ethyl salicylate, methyl 4-(hydroxy methyl) benzoate, methyl 4-hydroxy benzoate, ethyl 3-hydroxy benzoate, 4-methyl salicylate, ethyl salicylate, phenyl salicylate, propyl 4-hydroxy benzoate, phenyl 3-hydroxy naphthenoate, monoethylene glycol monobenzoate, diethylene glycol monobenzoate, and triethylene glycol monobenzoate; and alicyclic esters containing at least one hydroxy group, such as hydroxy butyl lactone. The required quantity of any of these monoester compounds having at least one hydroxy group is 0.001xcx9c5 mols, preferably 0.01xcx9c2 mols to one mol of magnesium.
Of the silicon compounds having at least one alkoxy group, which may be used as another electron donor in production of the catalyst, a compound which may be represented by the general formula: R1nSi(OR2)4xe2x88x92n(where R1 and R2 are hydrocarbons having 1xcx9c12 carbons, and xe2x80x9cnxe2x80x9d a natural number from 0 to 3) is preferable. In particular, such compounds may be used as: dimethyldimethoxysilane, dimethyidiethoxysilane, diphenyldimethoxysilane, methylphenyidimethoxysilane, diphenyldiethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, vinyltriethoxysilane, butyltriethoxysilane, phenyltriethoxysilane, ethyltriisopropoxysilane, vinyltributoxysilane, ethylsilicate, butylsilicate, methyltriaryloxysilane, etc. The quantity of above said silicon compound is preferably 0.05xcx9c3 mols, and more preferably 0.1xcx9c2 mols, to one mol of magnesium.
The temperature for contact-reaction of the liquid magnesium compound with the ester compound having at least one hydroxy group and the silicon compound having at least one alkoxy group is preferably 0xcx9c100xc2x0 C., and more preferably 10xcx9c70xc2x0 C.
For crystallization of the catalyst particles, the magnesium compound solution which has been reacted with an electron donor is then reacted with a mixture of a liquid titanium compound represented by the general formula Ti(OR)aX4xe2x88x92a (where R is a hydrocarbon group having 1 to 10 carbons, X a halogen atom, and a is a natural number from 0 to 4), and a silicon compound represented by the general formula RnSiCl4xe2x88x92n (where R is hydrogen; an alkyl group having 1xcx9c10 carbons; an alkoxy, haloalkyl, aryl group, or halosillyl having 1xcx9c8 carbons; or a halosillylalkyl group; and n a natural number from 0 to 4).
Examples of titanium compounds which satisfy the above general formula Ti(OR)aX4xe2x88x92a include: tetrahalogenated titaniums, such as TiCl4, TiBr4, and TiI4; tri-halogenated alkoxy titaniums, such as Ti(OCH3)Cl3, Ti(OC2H5)Cl3, Ti(OC2H5)Br3, and Ti(O(i-C4H3)Br3; dihalogenated alkoxy titaniums, such as Ti(OCH3)2Cl2, Ti(OC2H5)2Cl2, Ti(O(i-C4H9))2Cl2, and Ti(OC2H5)2Br2; and tetraalkoxy titaniums, such as Ti(OCH3)4, Ti(OC2H5)4, or Ti(OC4H9)4. Mixtures of the above titanium compounds may also be used effectively. The preferable titanium compounds are halogen-containing compounds, and the more preferable are titanium tetrachlorides.
Examples of silicon compounds which satisfy the above general formula RnSiCl4xe2x88x92n include: silicon tetrachloride; trichlorosilanes, such as methyltrichlorosilane, ethyltrichlorosilane, and phenyltrichlorosilane; dichlorosilanes, such as dimethyldichlorosilane, diethyldichlorosilane, diphenyldichlorosilane, and methylphenyldichlorosilane; and monochlorosilanes, such as trimethylchlorosilane. Mixtures of these silicon compounds may also be used. The preferable silicon compound is silicon tetrachloride.
The quantity of the mixture of a titanium compound and a silicon compound used for crystallization of the magnesium compound solution is preferably 0.1xcx9c200 mols to one mol of the magnesium compound, more preferably 0.1xcx9c100 mols, and still more preferably 0.2xcx9c80 mols. The molar ratio of titanium compound and silicon compound in the mixture is adequately 0.05xcx9c0.95, or more preferably 0.1xcx9c0.8. The shape and size of the crystallized solid constituent vary according to the conditions at the time of reaction of the magnesium compound solution and the mixture of titanium and silicon compounds. Therefore, the reaction of the magnesium compound solution and the mixture of titanium and silicon compounds is performed at a sufficiently low temperature, for formation of the solid constituent, preferably a contact-reaction at xe2x88x9270xc2x0 C.xcx9c70xc2x0 C., more preferably at xe2x88x9250xc2x0 C.xcx9c50xc2x0 C. After the contact-reaction, the temperature is gradually raised and the reaction is let to continue at 50xc2x0 C.xcx9c150xc2x0 C. for 0.5 hours to five hours.
The solid complex catalyst particles thus obtained may be further reacted with a titanium compound. The titanium compound for this further reaction is preferably a titanium halide, or a halogenated alkoxy titanium containing 1xcx9c20 carbons in the alkoxy group. A mixture of these may at times be used. Of these, titanium halides and halogenated alkoxy titaniums having 1xcx9c8 carbons in the alkoxy group are the more preferable, and yet more preferable are titanium tetrahalides.
The solid titanium catalyst may be profitably used in polymerization and copolymerization of ethylene. It is especially useful in homo-polymerization of ethylene and copolymerization of ethylene with (xcex1-olefin having three or more carbons, such as propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, and 1-hexene.
The polymerization reaction is for preparation of ethylene polymers or copolymers with the use of (1) the aforesaid solid titanium catalyst made from magnesium, titanium, a halogen, and an electron donor; (2) an organic metal compound of Group 2, 12, or 13 on the periodic table of elements; and (3) in the presence of an alkoxy silane compound as an external electron donor.
The aforesaid solid titanium catalyst can also be used to pre-polymerize ethylene or (xcex1-olefin, prior to use as constituent in a polymerization reaction. The pre-polymerization can be performed in the presence of a hydrocarbon solvent like hexane, or else at a sufficiently low temperature and under the pressure conditions of ethylene or xcex1-olefin in the presence of the aforesaid catalyst constituents and such an organic aluminum compound as triethylaluminum. Pre-polymerization makes catalyst granules wrapped in polymers to maintain the shape of the catalyst and thus helps to better the shape of the polymer after polymerization. The ratio in weight of polymer to catalyst after the pre-polymerization is usually 0.1:1xcx9c20:1.
Examples of organic metal compounds useful in the polymerization reaction may be represented by the general formula: MRn, where M is a metal of Groups 2, 12, or 13 on the periodic table of elements, such as magnesium, calcium, zinc, boron, aluminum or gallium; R is an alkyl groups having 1 to 20 carbons, such as methyl, ethyl, butyl, hexyl, octyl, or decyl; and n is the valence of the metal atom. The more preferable organic metal compounds include: trialkylaluminums containing an alkyl group of 1 to 6 carbons, such as triethylaluminum and triisobutylaluminum. Their mixtures are also commendable. In some cases organic aluminum compounds containing one or more halogens or hydride groups, such as ethylaluminum dichloride, diethylaluminum chloride, ethylaluminum sesquichloride, or diisobutylaluminum hydride may be used. Mixtures of these organic metal compounds are also usable.
Generally, to secure the catalyst""s best activity and the resultant polymer""s best stereo-regularity in polymerization of xcex1-olefin, and especially of propylene, many external electron donors are used. They include organic compounds containing atoms of oxygen, silicon, nitrogen, sulfur, and phosphorus such as organic acids, organic acid anhydrides, organic acid esters, alcohols, ethers, aldehydes, ketones, silanes, amines, amine oxides, amides, diols, ester phosphates, and mixtures of these. The electron donors useful in preparation of ethylene polymers having a narrow molecular weight distribution include: organic silicon compounds having an alkoxy group. These can be represented by the general formula: R1aSi(OR2)4xe2x88x92a, where R1 and R2 independently are alky groups containing 1xcx9c20 carbons, alicyclic groups, or an aryl groups; and a is a natural number 1 to 3. Examples of organic silicon compounds having the general formula R1aSi(OR2)4xe2x88x92a include: aromatic silanes, such as diphenylmethoxysilane, phenyltrimethoxysilane, phenylethylmethoxysilane, phenylmethyldimethoxysilane; aliphatic silanes such as isobutyltrimethoxysilane, diisobutyldimethoxysilane, diisopropyldimethoxysilane, di-t-butyldimethoxysilane, t-butyltrimethoxysilane, cyclohexylmethyldimethoxysilane, dicyclopentyldimethoxysilane, dicyclohexyldimethoxysilane, 2-novonantriethoxysilane, vinyltriethoxysilane; and their mixtures. Of these silane compounds, alkylalkoxysilanes such as diisobutyldimethoxysilane; and cycloalkyldialkoxysilanes such as dicyclopentyldimethoxysilane have proven effective.
The polymerization reaction may be performed in the gas phase, in bulk in the absence of an organic solvent, or in a liquid slurry in the presence of an organic solvent. The reactions, however, are performed in the absence of oxygen, water, or any compounds that may act as catalytic poison.
In the case of liquid slurry polymerization, the preferable concentration of the solid titanium catalyst (1) is about 0.001xcx9c5 Mmols in terms of the number of the titanium atoms per one liter of the solvent, more preferably about 0.001xcx9c0.5 Mmols. For the solvent, alkanes or cycloalkanes, such as pentane, hexane, heptane, n-octane, isooctane, cyclohexane, and methylcyclohexane; alkylaromatics, such as toluene, xylene, ethylbenzene, isopropylbenzene, ethyltoluene, n-propylbenzene, and diethylbenzene; and halogenated aromatics, such as chlorobenzene, chloronaphthalene, or orthodichlorobenzene; and mixtures of these, may be useful.
In the case of gaseous polymerization, the quantity of the solid titanium catalyst (1), in terms of the number of titanium atoms in the catalyst per liter of polymerization reactor vessel, is about 0.001xcx9c5 Mmols, preferably about 0.001xcx9c1.0 Mmols, still more preferably about 0.01xcx9c0.5 Mmols.
The preferable concentration of the organic metal compound (2) is about 1xcx9c2000 mols, more preferably about 5xcx9c500 mols, in terms of the number of the atoms of the organic metal to one mol of the titanium atoms in the catalyst (1).
The concentration of the alkoxy silane compound (3) is preferably 0.01xcx9c40 mols and more preferably about 0.05xcx9c30 mols in terms of the number of the silicon atoms per mol of the organic metal""s atoms in the organic metal compound.
To secure a high speed in polymerization the reaction is performed at a sufficiently high temperature regardless of the polymerization process itself. Generally, about 20xcx9c200xc2x0 C. is adequate, and 20xcx9c95xc2x0 C. is preferable. The pressure of a monomer is adequately 1 atm to 100 atm, and more preferably 2xcx9c50 atm.
The molecular weights of the polymer examples below are given in terms of the broadly known American Society For Testing and Materials (ASTM) D 1238. In ASTM, the smaller the molecular weights are the larger the ASTM values are. The molecular weight distribution was obtained through measurement by Gel Permeation Chromatography (GPC), a measurement method widely adopted in the art.